Conventionally, a knitted fabric has been knitted by a weft knitting machine by repetitively carrying out an operation for moving a knitting needle into a knitted fabric knitting region such as a needle bed gap and moving the knitting needle backward upon receipt of the supply of a knitting yarn, and knocking over the previously knitted loop to form a new knitted loop. A sinker is disposed on both sides of the knitting needle and has a function of supporting the knitting yarn pulled in by the knitting needle which is moved backward.
For a sinker, there has also been used a movable sinker which is pivotally displaced about the vicinity of the needle bed gap side of a needle bed set to be a support point and is displaced by a cam mechanism provided on a carriage in such a manner that a tip is moved forward into the needle bed gap and is moved backward from the needle bed gap as is disclosed in Japanese Examined Patent Publication JP-B2 5-83657(1993), for example. In this case, two separated pressing cams are provided in the carriage. The tip of the movable sinker is moved forward and backward with respect to the needle bed gap side interlockingly with the movement of the carriage by the pivotally displacing operation carried out by the action of one of the pressing cams. Consequently, it is possible to press the knitted fabric or to move backward from the needle bed gap, thereby preventing a mechanical interference with the other portions through the small needle bed gap. A spring energization is also carried out over the movable sinker. When a reactive force applied from the knitting yarn is greater than an energizing force applied from a spring, there is room for the tip of the movable sinker to be moved backward from the needle bed gap. Consequently, it is also possible to prevent an excessive tension from acting on the knitting yarn.
The spring energization of the sinker also has the function of pressing the knitted fabric downward. In a state in which the sinker is not moved forward and backward by means of the carriage, accordingly, the sinker is set into a forward moving state into the needle bed gap. In a weft knitting machine in which front and rear needle beds are opposed to each other at a needle port, it is possible to carry out a racking operation for shifting the relative positional relationship of the needle bed back and forth in the longitudinal direction of the needle bed gap. When the state in which the sinker is moved forward into the needle bed gap is maintained in the racking operation, the tip of the sinker might be caught on the knitted fabric held on the opposed needle bed, resulting in a damage. For a countermeasure, a mechanism for moving the sinker backward from the needle bed gap and stopping the same sinker as is disclosed in Japanese Unexamined Patent Publication JP-A 9-31806(1997), for example.
As described in the JP-B5-83657, the sinker to be energized by a spring also has the function of beingmoved forward into a needle bed gap and pressing a knitted loop in order to press the same knitted loop downward. In the sinker unit described in the JP-B2 5-83657, the amount of press-in of the knitted fabric through the sinker is always constant and an operation for moving the sinker forward and backward is carried out by means of the cam mounted on the carriage in a timing in which the sinker is to be moved backward from the needle bed gap. In the movable sinker described in the JP-A 9-31806, it is possible to move the movable sinker backward to such a stop position as not to press a knitted fabric in by the action of the carriage.
When the quality of a knitting yarn to be used for knitting, the number of knit stitches of a knitted fabric and a knitting texture are varied, however, the amount of press-in of the knitted fabric through an optimum sinker is also different. In the sinker described in the JP-B2 5-83657, a maximum amount of press-in is constant. In the movable sinker described in the JP-A 9-31806, also in the case in which the stop state can be held by a backward movement from the needle bed gap, the amount of press-in in the forward movement into the needle bed gap is constant so that the maximum amount of press-in cannot be regulated.